Connected: An Internet Encyclopedia
RFC 1812 - 10.2.2 Address and Prefix Initialization

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### 10.2.2 Address and Prefix Initialization

A router MUST allow its IP addresses and their address masks or prefix lengths to be statically configured and saved in non-volatile storage.

A router MAY obtain its IP addresses and their corresponding address masks dynamically as a side effect of the system initialization process (see Section 10.2.3]);

If the dynamic method is provided, the choice of method to be used in a particular router MUST be configurable.

As was described in Section [4.2.2.11], IP addresses are not permitted to have the value 0 or -1 in the <Host-number> or <Network-prefix> fields. Therefore, a router SHOULD NOT allow an IP address or address mask to be set to a value that would make any of the these fields above have the value zero or -1.

DISCUSSION

  It is possible using arbitrary address masks to create situations in which routing is ambiguous (i.e., two routes with different but equally specific subnet masks match a particular destination address). This is one of the strongest arguments for the use of network prefixes, and the reason the use of discontiguous subnet masks is not permitted.

A router SHOULD make the following checks on any address mask it installs:

- The mask is neither all ones nor all zeroes (the prefix length is neither zero nor 32).

- The bits which correspond to the network prefix part of the address are all set to 1.

- The bits that correspond to the network prefix are contiguous.

DISCUSSION

  The masks associated with routes are also sometimes called subnet masks, this test should not be applied to them.

Next: 10.2.3 Network Booting using BOOTP and TFTP

Connected: An Internet Encyclopedia
RFC 1812 - 10.2.2 Address and Prefix Initialization